线程2——条件变量

动态创建条件变量

int pthread_cond_init(pthread_cond_t *cond, pthread_condattr_t *cond_attr);

注销一个条件变量

int pthread_cond_destroy(pthread_cond_t *cond);

无条件等待

int pthread_cond_wait(pthread_cond_t *cond, pthread_mutex_t *mutex);

计时等待

int pthread_cond_timedwait(pthread_cond_t *cond, pthread_mutex_t *mutex, const struct timespec*abstime);

发送单个条件变量成立信号

int pthread_cond_signal(pthread_cond_t *cond)

广播条件变量成立信号

int pthread_cond_ broadcast (pthread_cond_t *cond)

 1 #include <pthread.h>
 2 #include <stdio.h>
 3 #include <unistd.h>
 4 #include <stdlib.h>
 5 #include <sys/time.h>
 6 //声明两个线程
 7 void* task1(void *arg);
 8 void* task2(void *arg);
 9 pthread_t tid[3];                    //线程的3个指针
10 pthread_mutex_t lock;                //互斥锁指针
11 pthread_cond_t cond;                //条件变量指针
12 int main(void)
13 {
14     int ret;
15     
16     //初始化互斥锁和条件变量
17     pthread_mutex_init(&lock,NULL);
18     pthread_cond_init(&cond,NULL);
19     //创建2个线程
20     pthread_create(&tid[0],NULL,task1,NULL);
21     pthread_create(&tid[1],NULL,task2,NULL);
22     //等待
23     pthread_join(tid[0],NULL);
24     pthread_join(tid[1],NULL);
25 
26     printf("Main:ALL new threads end
");
27     //销毁互斥锁
28     pthread_mutex_destroy(&lock);
29     pthread_exit(NULL);
30 }
31 
32 void* task1(void *arg)
33 {
34     struct timeval now;
35     /*
36      struct timeval 
37         {
38           time_t       tv_sec;    //  seconds 秒
39           suseconds_t   tv_usec; // microseconds 毫秒
40         };
41     */
42     struct timespec outtime;
43     /*
44     struct timespec 
45         {
46             time_t tv_sec; // seconds 秒
47             long tv_nsec; // and nanoseconds 纳秒 
48         };
49     */
50     printf("I am task1
");
51     pthread_mutex_lock(&lock);        //上锁
52     printf("task1: wait max time is 5s
");
53     gettimeofday(&now, NULL);        //返回自1970-01-01 00:00:00到现在经历的秒数
54     outtime.tv_sec = now.tv_sec + 5; 
55     outtime.tv_nsec = now.tv_usec * 1000;
56     pthread_cond_timedwait(&cond, &lock, &outtime);//线程1等待条件变量，最多等待5s
57     printf("task1: coutinue run
");
58     printf("task1: ready to pthread_exit
");
59     
60     pthread_exit(NULL);
61 }
62 
63 
64 void* task2(void *arg)
65 {
66     printf("I am task2
");
67     sleep(3);      //线程2休眠3s后激活条件变量
68     printf("task2: ready to signal the cond
");
69     pthread_cond_signal(&cond);    //发送变量成立信号 用来激活条件变量
70     printf("task2: ready to pthread_exit
");
71     pthread_exit(NULL);
72 }

运行后代码如下

1 k1: wait max time is 5s
2 I am task2
3 task2: ready to signal the cond
4 task2: ready to pthread_exit
5 task1: coutinue run
6 task1: ready to pthread_exit
7 Main:ALL new threads end

先运行task1，触发条件变量，跳到task2激活，执行task2的两句话，然后再回到task1执行两句话，最后回到主函数

计时等待：pthread_cond_timedwait()；用法：

1 struct timeval now;
2 struct timespec outtime;
3 gettimeofday(&now, NULL);//获取当前时间
4 outtime.tv_sec = now.tv_sec + 5; //设定唤醒的绝对时间是当前时间+5s
5 outtime.tv_nsec = now.tv_usec * 1000;
6 pthread_cond_timedwait(&cond, &lock, &outtime);

用到的两个结构体

 1 struct timeval{  
 2     long int tv_sec; // 秒数  
 3     long int tv_usec; // 微秒数  
 4 }  
 5 
 6 
 7 
 8 struct timespec {
 9     time_t tv_sec; // seconds 秒 
10     long tv_nsec; // and nanoseconds 毫秒 
11 };